Medical diagnostic imaging is widely used for the examination of body cavities. A prerequisite for the imaging of body cavities is the instillation of a fluid in order to obtain a fluid-filled cavity. In these fluid-filled cavities, the fluid has two functions (1) to open up the cavity from its “collapsed” state (distension) and (2) to enhance the contrast of the image of the body cavity. Conventionally, water or watery fluids are used for distension and contrast imaging. Sometimes, this is combined with the generation of bubbles, to further increase contrast. For example, U.S. Pat. No. 4,681,119 describes novel compositions and methods for generating microbubbles in a liquid-filled cavity for enhancing ultrasonic images of such cavities.
Since water easily leaks from the body cavity, it has to be replenished continuously during imaging. This is one of the big disadvantages of the use of water as a contrast medium during examination or imaging. This disadvantage may be solved partly by using liquid installation devices which reduce the leakage. For instance, a catheter equipped with an inflatable balloon may be used. However, this is not very convenient for the patient.
WO 03/094710 suggests a solid or semi-solid phase-shifting medium of pH 7.4 for providing contrast enhancement and/or distention of the subject body or organ cavity during imaging, radiographic visualisation or similar medical examinations. The medium is designed to have high, but undefined, viscosity initially and then to liquefy or lose viscosity after a period of time in order to facilitate easy removal of the medium from the body cavity. This phase-shifting medium includes polymers such as starches, and colloidal clays, such as bentonite and tragacanth, in order to achieve the phase shift. Disadvantage of such ingredients is that the additives, such as starches, will interfere with image formation.
WO 92/00707 describes an opthalmic gel suspension for dry eye application containing lightly cross-linked polymers of acrylic acid with a particle size of not more than 50 micrometer. These polymers are formulated with one or more opthalmic demulgents, such as cellulose derivatives, polyvinyl alcohol or polyvinylpyrrolidone, or opthalmic vasoconstrictors, and optionally with opthalmic adjuvants or additives, into gel suspensions. The opthalmic suspensions have a pH of about 6.6-8.0 and a viscosity of 500 to 4000 centipoise. Due to the acrylic acid polymers, these compositions will not be the preferred choice for imaging body cavities. In addition, the particles in these opthalmic gel suspension will interfere with image formation.
Therefore, there is a need for alternative contrast agents which do not easily leak from the body cavity during examination and which enable high quality images without jeopardising the safety of the patient.